metadata_dictionary: Fix crash on null list item in an uri_field.

swh/indexer/metadata_dictionary/base.py

@@ -243,7 +243,8 @@ class DictMapping(BaseMapping):
                     graph.add((root, codemeta_key, rdflib.URIRef(v)))
                 elif k in self.uri_fields and isinstance(v, list):
                     for item in v:
-                        graph.add((root, codemeta_key, rdflib.URIRef(item)))
+                        if isinstance(item, str):
+                            graph.add((root, codemeta_key, rdflib.URIRef(item)))
                 else:
                     continue
 

swh/indexer/tests/metadata_dictionary/test_npm.py

@@ -160,6 +160,28 @@ def test_index_content_metadata_npm(storage, obj_storage):
     assert expected_results == results
 
 
+def test_npm_null_list_item_normalization():
+    package_json = b"""{
+        "name": "foo",
+        "keywords": [
+            "foo",
+            null
+        ],
+        "homepage": [
+            "http://example.org/",
+            null
+        ]
+    }"""
+    result = MAPPINGS["NpmMapping"]().translate(package_json)
+    assert result == {
+        "@context": "https://doi.org/10.5063/schema/codemeta-2.0",
+        "name": "foo",
+        "type": "SoftwareSourceCode",
+        "url": "http://example.org/",
+        "keywords": "foo",
+    }
+
+
 def test_npm_bugs_normalization():
     # valid dictionary
     package_json = b"""{